This invention relates to a fuel-cell device which is permitted to stop by promptly replacing a fuel gas and air with nitrogen gas at the time of the urgent stop of the device or the suspension of electric power, without affording a great differential pressure fluctuation between the fuel gas and air of a fuel cell stack.
A prior-art device of the pertinent type is, for example, a fuel-cell device which is disclosed in the official gazette of Japanese Patent Application Laid-open No. 58-163182 and the arrangement of which is shown in FIG. 1. Referring to the figure, numeral 1 designates a cell vessel which receives therein a fuel cell stack 2 furnished with inlet and outlet manifolds for fuel and air. A fuel flow control valve 3 serves to supply the fuel to the fuel cell stack 2, while a fuel differential pressure control valve 4 is disposed on the excess fuel outlet side of the fuel cell stack 2. An air flow control valve 5 supplies the air, while an air differential pressure control valve 6 is disposed on the excess air outlet side of the fuel cell stack 2. A nitrogen flow control valve 7 supplies nitrogen to the cell vessel 1, while a case nitrogen pressure control valve 8 controls a nitrogen pressure in the cell vessel 1. Numerals 9 and 10 indicate switching valves, such as magnet valves, which are disposed in the vessel 1.
Next, the operation of the prior-art fuel-cell device will be described. The fuel flows into the fuel cell stack 2 via the fuel flow control valve 3, and it reacts in the cell portion to become excess fuel, which egresses from the fuel differential pressure control valve 4. On the other hand, the air flows into the fuel cell stack 2 via the air flow control valve 5 and has oxygen consumed in the cell portion, whereupon the resulting excess air egresses from the air differential pressure control valve 6. The nitrogen flows into the cell vessel 1 receiving the fuel cell stack 2 therein via the nitrogen flow control valve 7, and it egresses from the nitrogen pressure control valve 8 located on the outlet side of the cell vessel 1. A cell operating pressure is set by the nitrogen pressure control valve 8. An air pressure in the fuel cell stack 2 is set somewhat lower than a nitrogen pressure in the cell vessel 1, and a fuel pressure in the same is set still somewhat lower than the air pressure, thereby to prevent the contact reaction between the fuel and the air.
During the operation of the fuel cell, the switching valves 9 and 10 arranged in the cell vessel 1 are held closed. When stopping the fuel cell, the switching valves 9 and 10 are first opened, and the fuel flow control valve 3 and the air flow control valve 5 are subsequently closed. After the inner atmosphere of the fuel cell stack 2 is replaced with nitrogen, the fuel differential pressure control valve 4 and the air differential pressure control valve 6 having been fully open are closed. Lastly, the nitrogen flow control valve 7 and the nitrogen pressure control valve 8 are controlled to lower the pressure in the cell vessel 1 down to the normal pressure.
When starting the fuel cell, the fuel cell stack 2 is supplied with the fuel and the air in the order reverse to that for the stop so as to generate electric power.
The prior-art fuel-cell device is constructed as described above. Therefore, when the fuel cell is to be stopped urgently, the nitrogen pressure in the cell vessel 1 needs to be held at a fixed value while the fuel and air lines are subjected to the nitrogen replacement, so that the nitrogen flow control valve 7 of wide flow control range is necessitated. In addition, when electric power has suspended, the nitrogen flow control valve 7 is held in the state of replacing the fuel and the air with the nitrogen (the open state), so that a master valve for supplying the nitrogen gas needs to be closed after a fixed period of time (after the interior of the cell has been replaced with nitrogen).
Moreover, the provision of the switching valves 9 and 10 in the cell vessel 1 is inconvenient for maintenance.